Gamma-valerolactone (5-methylbutyrolactone, in the context of the invention also referred to as “valerolactone”) is a valuable compound which is inter alia used in the production of adipic acid (1,6-hexanedioic acid) which is an important precursor for inter alia the production of polyamides such as polyamide 6,6 (also referred to as “Nylon”) or polyamide 4,6 (also referred to as “Stanyl”). Further, esters of adipic acid may be used in plasticisers, lubricants, solvents and in a variety of polyurethane resins. Other uses of adipic acid are as food acidulants, applications in adhesives, insecticides, tanning and dyeing.
US2003/0055270 discloses a process to produce valerolactone from levulinic acid using a solid Ru catalyst, e.g. supported on carbon. WO2012175439 discloses a process to produce valerolactone from levulinic acid using a solid Ru catalyst, e.g. supported on carbon whereby the hydrogenation reaction is done in the presence of at least 0.08% (w/w) water relative to the amount of levulinic acid. Other references to the hydrogenation of levulinic acid are Hasan Mehdi et al: “Integration of homogeneous and heterogeneous catalytic processes for a multi-step conversion of biomass: from sucrose to levulinic acid, valerolactone, 1,4-pentanediol, 2-methyl-tetrahydrofuran, and alkanes”, Topics in Catalysis, Kluwer Academic Publishers—Plenum publishers, NE, vol. 48, no. 1-4, 5 Apr. 2008, pages 49-54; and M. Chalid et al: “Experimental and kinetic modeling studies on the biphasic hydrogenation of levulinic acid to [gamma]-valerolactone using a homogeneous water-soluble Ru-(TPPTS) catalyst”, Journal of Molecular Catalysis A: Chemical, vol. 341, no. 1-2, 1 May 2011, pages 14-21.
Levulinic acid (LA) is a starting molecule for the synthesis of commercially important compounds. Commercially, LA is made from furfuryl alcohol. It is also possible to produce LA by acid hydrolysis of biomass although this is not commercially practiced (see for example U.S. Pat. No. 5,608,105, U.S. Pat. No. 8,138,371, US2010/312006, U.S. Pat. No. 4,897,497, U.S. Pat. No. 6,054,611, and “The Biofine Process—Production of Levulinic Acid, Furfuraldehyde, and Formic Acid from Lignocellulosic Feedstocks”, D. J. Hayes, S. Fitzpatrick, M. H. B. Hayes, J. R. H. Ross, in Biorefineries—Industrial Processes and Products, Status Quo and Future Directions, B. Kamm, P R. Gruber, M. Kamm, eds., Wiley-VCH, Weinheim, Germany, 2010, p 139-164).
Prior to the hydrogenation reaction the catalyst can be activated by pretreatment with a reductant. US2004/254384 relates to the production of gamma valerolactone from levulinic acid using a solid Ru catalyst. The catalyst is reduced in hydrogen for 2 hours at 400° C. prior to use. In APPLIED CATALYSIS A: GENERAL, vol. 272, no. 1-2, (2004), p. 249-256 is described a repeated batch process for the hydrogenation of levulinic acid into gamma valerolactone using a solid ruthenium catalyst (Ru/C). The catalyst is reduced in hydrogen for 2 hours at 400° C. prior to use. In US2012/302766 is described the hydrogenation of levulinic acid into gamma valerolactone using a solid ruthenium catalyst (Ru—Sn/C) and water as solvent uses a Ru/Sn catalyst. The catalyst is reduced for 3 hours at 723° K (450° C.) before use. In CN102658131A is described the hydrogenation of levulinic acid into gamma valerolactone using a solid ruthenium catalyst and water as solvent. The catalyst is purged with hydrogen for 2 hours before use. US2010/324310 describes a batch process for the hydrogenation of levulinic acid into gamma valerolactone using a solid ruthenium catalyst (Ru/C) and water as solvent. The catalyst is reduced with hydrogen at 673° K (400° C.) before use. All these processes use pre-treatment with H2 in the gasphase at high temperatures which consumes a lot of energy and requires a separate reactor of dedicated design. This invention is aimed at overcoming at least some of these problems.